State-of-the-art (SOA) optical communication link efficiencies are bumping against the theoretical limits of channel capacity, with more than one demonstration of links transferring data reliably at an average rate of several bits per detected photon. However, despite the great strides in link efficiency, conventional receiver pointing, acquisition, and tracking (PAT) implementations are often complex, and the size weight and power (SWaP) of PAT subsystems is often a barrier to adoption of optical communication in SWaP-constrained systems. A major reason PAT is so challenging is that the detectors must have narrow fields of view, typically 1 mrad or less, to suppress background illumination. At the same time, initial acquisition of a beacon or optical communication transmitter may require searching a solid angle that spans several degrees or more.
The diametrically opposed requirements of a narrow field of view (NFOV) for detection and decoding of communication data and wide field of view (WFOV) for acquisition are typically satisfied by precision mechanical scanning the NFOV detector, guided by a WFOV acquisition detector (e.g., a quad cell). The handoff from WFOV detection to NFOV acquisition and tracking increases the latency in establishing a communication link. It also significantly increases the SWaP, cost, and complexity of the receiver, often eliminating free-space optical communications from consideration for SWaP-constrained systems.